This invention pertains to the hydrogenation of monosaccharides such as glucose to produce sorbitol product using a continuous fixed bed catalytic process.
Sorbitol is produced commercially from glucose through either electrolytic reduction, or enzymatic, or catalytic hydrogenation processes. Because of economic reasons, the catalytic hydrogenation processes for making sorbitol have been substituted for the other two processes. A batch autoclave process using a Raney nickel pwoder catalyst is presently the major glucose hydrogenation process used in industry. However, batch processes have the disadvantage that new catalyst must be made in situ for each batch of feed. Another drawback of batch processes is that their capacity relative to reaction volume is very small, which causes a need for large storage tanks. Also the consumption of steam and power and labor requirements are relatively high. To overcome these batch process handicaps, a continuous hydrogenation process using a suspended Raney nickel catalyst and two stirred tank reactors in series was developed and is used by some companies, as described by Haideggar in Industrial & Engineering Chemistry, Vol. 7, No. 1, January 1968. However, a disadvantage is the requriement to filter off the catalyst from the product in order to recycle the catalyst, and doing this without reducing the catalyst activity.
It has been further reported by this Haidegger article that VEB Deutsches Hydrierwerk uses a continuous catalytic fixed-bed process for converting glucose to sorbitol at Rodleben, East Germany. The catalyst used is a supported mixed copper/nickel catalyst. However, this process requires a relatively high hydrogen pressure of almost 3000 psig, a low liquid hourly space velocity of 1.0, and a low concentration of glucose in the aqueous feed of 25%, which are deficiencies for the process. It was reported again by Haidegger that local overheating of the catalyst surface due to the heat of the hyrogenation reaction led to isomerization, cracking, and carmel formation. The product sorbitol contained a significant amount of mannitol. Therefore, further process improvements for the catalytic hydrogenation of glucose to produce high conversion to sorbitol product are desired.